1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for determining execution or non-execution of a location update process caused by a variation of a paging group in a broadband wireless communication system.
2. Description of the Related Art
In the 4th Generation (4G) communication system, which is a next generation communication system, intensive research is being conducted to provide users with services having various Qualities-of-Service (QoSs) at a data rate of about 100 Mbps. In particular, a study of the 4 G communication system is being made to support high-speed services as a way of guaranteeing mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system. An exemplary 4 G communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
In the 802.16 system, a plurality of Base Stations (BSs) compose a logical group called a paging group. The paging group is a unit representing a location of an idle mode Mobile Station (MS). That is, if there is a downlink traffic for an idle mode MS, all BSs within a paging group corresponding to the idle mode MS attempt to page the idle mode MS. The paging group is determined when a system is designed. The paging group is large enough to keep a moving idle mode MS within the same paging group during a defined amount of time and is small enough to keep a paging load at a desired level.
In order to inform an idle mode MS of a paging group the MS currently belongs to, all BSs periodically transmit MOBile PAGing ADVertisement (MOB_PAG ADV) messages including Paging Group IDentifiers (PG_IDs). The MOB_PAG_ADV messages include identification information on the BSs' own corresponding paging groups. Because the MOB_PAG_ADV message is transmitted through a predefined resource at a preset period, the idle mode MS can receive the MOB_PAG_ADV message. Accordingly, the idle mode MS determines if there is a change of a paging group by identifying the PG_ID included in the received MOB_PAG_ADV message and compares the identified PG_ID with a previously identified PG_ID. Upon determining that there is a change of a paging group, the idle mode MS performs a location update process as illustrated in FIG. 1. FIG. 1 is a ladder diagram illustrating a signal exchange occurring upon execution of a location update process in a broadband wireless communication system according to the conventional art. Referring to FIG. 1, the idle mode MS performs the location update process by receiving a MOB_PAG_ADV message and recognizing a change of a paging group in step 101. The idle MS then transmits a message for a location update (i.e., a RaNGing REQuest (RNG_REQ) message for the location update) to a BS in step 103. Thereafter, the idle MS receives a RaNGing ReSPonse (RNG_RSP) message from the BS in step 105.
FIGS. 2A and 2B illustrate examples of received signal strengths from a BS A and a BS B measured by an MS when the MS moves between cells of the BS A and the BS B which belong to different paging groups. In FIG. 2A, an MS experiences no problems with receiving a MOB_PAG_ADV message, recognizing a change of a paging group at timing A (211), transmitting an RNG_REQ message for a location update process to the BS B at timing B (213), and receiving an RNG_RSP message from the BS B at timing C (215). On the other hand, in FIG. 2B, an MS receives a MOB_PAG_ADV message, recognizes a change of a paging group at timing A (231) and transmits an RNG_REQ message to the BS B at timing B (233). However, the RNG_REQ message may be lost because of a deteriorated channel state at timing B (233). Alternately, although the RNG_REQ message is successfully received at timing B (233), an RNG_RSP message transmitted at timing C (235) may be lost. That is, the location update of the MS fulls.
As described above, when an idle mode MS performs a location update process when moving between cells, a variation of a channel state with a BS of a target cell may lead to a failure of the location update process. The aforementioned failure leads to an unnecessary power consumption of an MS and a waste of radio resources due to a loss of a message. Therefore, there is a need to improve a success rate of a location update process.